Since the initial discovery of polymer organic light emitting diodes (PLEDs), substantial developments have occurred that have led to a fundamental understanding of their operation as well as the development of practical devices. Multi-component polymer and organic LEDs that exploit energy transfer among various emitting chromophores distributed within the active matrix allow precise control of emission energies. These multi-component devices have been designed using a variety of approaches that include direct blending of two polymers, the use of intimately mixed polymer layers (such as polyelectrolyte multilayers, thin coated films, laminates, etc.) and the incorporation of emitting metal complexes within polymer host matrices. Examples of the latter include the use of blue emitting derivatized poly(p-phenylene)s doped with Eu complexes to produce red light emission, blending of poly(p-phenylene vinylene)s with a phosphorescent Pt(II)-porphyrin, and luminescent Ir(III) complexes dispersed in small-molecule host matrices. Due to their unique electronic structure, many lanthanide ions luminesce in the near-IR. Taking advantage of this phenomenon, films of neat lanthanide complexes, a blend of an Er(III) complex in poly(vinylcarbazole), and a blend of a Nd-lissamine complex dispersed in a poly(fluorene-benzothiadiazole) co-polymer host have been used as the emitting materials to afford electroluminescent devices that emit in the near-IR.